Tomographic image capturing devices are put into practical use. Such a device captures tomographic images of an ocular fundus using the principle of optical coherence tomography (OCT).
In a process of treatment for a patient who suffers from lesion of ocular fundus, the volume of the site of lesion may have to be regularly measured to estimate the medicinal effect. Measuring the volume of the site of lesion using tomographic images includes configuring a three-dimensional tomographic image from a plurality of B-scan images (tomographic images) obtained by scanning the ocular fundus, manually setting contours of the site of lesion in the B-scan images, and calculating the area of the site of lesion using the number of pixels. The number of pixels of the calculated area of the site of lesion in each B-scan image is then accumulated and multiplied by the actual area of one pixel and the volume of the site of lesion can thereby be obtained.
However, the actual area of one pixel is different among subjects. This is because, if the scanning width (angle of field) is the same despite different eye axial lengths of the subjects, the image region to be acquired varies. For example, in the case of a subject of myopia, the eye axial length is longer than that of a subject's eye having a normal diopter. Accordingly, the ocular fundus image obtained by scanning spans a wide range and the actual area of one pixel is larger than that of the subject having a normal diopter.
Patent Literature 1 discloses a scheme of scanning light on the ocular fundus of a subject's eye and receiving the reflected light to obtain the ocular fundus image. As described above, in the case of a subject's eye of myopia of which the eye axial length is long, if the scanning angle of field is the same as that for a subject's eye having a normal diopter, the ocular fundus is scanned within a wide range, so that the ocular fundus image to be obtained expands to have a larger area than that of the subject's eye having a normal diopter. Such a configuration is not problematic in an examination in which the change over time of the same subject is qualitatively evaluated, but comparison with others cannot be performed. In Patent Literature 1, therefore, information regarding the eye axial length of the subject's eye is acquired and the scanning angle is adjusted on the basis of the information such that the ocular fundus image becomes substantially the same as that of the subject's eye having a normal diopter. Such control allows the scanning range to be narrow in the case of an eye of myopia of which the eye axial length is long.